The transmittance and refractive index of transparent materials are two of the main concerns when the transparent materials are used in optical displays or modules. Research related to the refractive index of materials shows that refractivity may depend on the molecular weight, density, or molar refractivity of the materials. Those materials which have a higher density, larger molar refractivity, and smaller molar volume may have a higher refractivity.
In general, to increase the refractive index of the materials, chemical synthesis or organic-inorganic dispersion techniques are required. The chemical synthesis technique includes modifying the material by performing a chemical synthesis. For example, modifying the molecule structure to include aromatic rings, halogens, sulfur, or the like can increase the refractive index of the material. However, the chemical synthesis may result in worsening the transmittance and the thermal and yellowing resistance of the material.
The organic-inorganic dispersion technique includes adding nano-inorganic oxide having a high refractive index into a transparent organic material matrix. Since the nano-inorganic oxide and the organic material matrix tend to have incompatible interfaces and the nano-inorganic oxide particles tend to assemble with each other, an intensive mechanical shearing force is usually used in a dispersion process to evenly disperse the nano-inorganic oxide particles into the organic material matrix. However, when the material contains more than 50 wt % of the nano-inorganic oxide or when the thickness of the material is larger than 100 μm, the transmittance of the material will decrease notably. Therefore, the method can only be used to prepare a thin film but can not be used to form a bulk material having a larger thickness.
Therefore, a transparent material having good transmittance and high refractive index is required.